Hi Olof,
On Tue, Aug 26, 2014 at 7:14 PM, Olof Johansson <olof@xxxxxxxxx> wrote:
> Hi,
>
>
>
> On Tue, Aug 26, 2014 at 4:45 PM, David Riley <davidriley@xxxxxxxxxxxx> wrote:
>> This driver registers a restart handler to set a GPIO line high/low
>> to reset a board based on devicetree bindings.
>>
>> Signed-off-by: David Riley <davidriley@xxxxxxxxxxxx>
>> ---
>> .../devicetree/bindings/gpio/gpio-restart.txt | 48 +++++++
>> drivers/power/reset/Kconfig | 8 ++
>> drivers/power/reset/Makefile | 1 +
>> drivers/power/reset/gpio-restart.c | 142 +++++++++++++++++++++
>> 4 files changed, 199 insertions(+)
>> create mode 100644 Documentation/devicetree/bindings/gpio/gpio-restart.txt
>> create mode 100644 drivers/power/reset/gpio-restart.c
>>
>> diff --git a/Documentation/devicetree/bindings/gpio/gpio-restart.txt b/Documentation/devicetree/bindings/gpio/gpio-restart.txt
>> new file mode 100644
>> index 0000000..7cd58788
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/gpio/gpio-restart.txt
>> @@ -0,0 +1,48 @@
>> +Driver a GPIO line that can be used to restart the system as a
>> +restart handler.
>> +
>> +The driver supports both level triggered and edge triggered power off.
>> +At driver load time, the driver will request the given gpio line and
>> +install a restart handler. If the optional properties 'input' is
>> +not found, the GPIO line will be driven in the inactive state.
>> +Otherwise its configured as an input.
>> +
>> +When do_kernel_restart is called the various restart handlers will be tried
>> +in order.
>
> The above sentence documents the kernel behavior, not the hardware
> description/binding.
I've cleaned this up.
>
>> +The gpio is configured as an output, and drive active, so
>> +triggering a level triggered power off condition. This will also cause an
>> +inactive->active edge condition, so triggering positive edge triggered
>> +power off.
>
>> + After a delay of 100ms, the GPIO is set to inactive, thus
>> +causing an active->inactive edge, triggering negative edge triggered power
>> +off. After another 100ms delay the GPIO is driver active again. If the
>> +power is still on and the CPU still running after a 3000ms delay, a
>> +WARN_ON(1) is emitted.
>
> It's possible that this behavior is inadequate for some hardware in
> the future -- if so they can amend the binding (i.e. this comment is
> an attempt at preemptive bikeshed avoidance :)
Changed to be configurable at the request of Guenter.
>> +
>> +Required properties:
>> +- compatible : should be "gpio-restart".
>> +- gpios : The GPIO to set high/low, see "gpios property" in
>> + Documentation/devicetree/bindings/gpio/gpio.txt. If the pin should be
>> + low to power down the board set it to "Active Low", otherwise set
>> + gpio to "Active High".
>> +
>> +Optional properties:
>> +- input : Initially configure the GPIO line as an input. Only reconfigure
>> + it to an output when the machine_restart function is called. If this optional
>> + property is not specified, the GPIO is initialized as an output in its
>> + inactive state.
>
> Isn't this the same as configuring the pin as tristate? I think that
> should probably be controlled by pinmux setup instead?
I think this still needs to be usable independently of pinctrl and it
keeps consistency with gpio-poweroff.
>
>> +- priority : A priority ranging from 0 to 255 (default 128) according to
>> + the following guidelines:
>> + 0: Restart handler of last resort, with limited restart
>> + capabilities
>> + 128: Default restart handler; use if no other restart handler is
>> + expected to be available, and/or if restart functionality is
>> + sufficient to restart the entire system
>> + 255: Highest priority restart handler, will preempt all other
>> + restart handlers
>
> This is sort of leaking linux implementation, but it's also a useful
> feature to have in the description. It seems sane enough to me to use.
>
>> +
>> +Examples:
>> +
>> +gpio-restart {
>> + compatible = "gpio-restart";
>> + gpios = <&gpio 4 0>;
>> + priority = /bits/ 8 <200>;
>
> I think it makes sense to just have this as a regular cell instead of
> doing an 8-bit value -- it's how we normally handle these elsewhere.
Done.
>
>
> -Olof
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